Rapamycin is a macrolide antibiotic produced by Streptomyces hygroscopicus which was first characterized via its properties as an antifungal agent. It adversely affects the growth of fungi such as Candida albicans and Microsporum gypseum. Rapamycin, its preparation and its antibiotic activity were described in U.S. Pat. No. 3,929,992, issued Dec. 30, 1975 to Surendra Sehgal et al. In 1977 Martel, R. R. et al. reported on immunosuppressive properties of rapamycin against experimental allergic encephalitis and adjuvant arthritis in the Canadian Journal of Physiological Pharmacology, 55, 48-51 (1977). In 1989, Calne, R. Y. et al. in Lancet, 1989, no. 2, p. 227 and Morris, R. E. and Meiser, B. M. in Medicinal Science Research, 1989, No. 17, P. 609-10, separately reported on the effectiveness of raparnycin in inhibiting rejection in vivo in allograft transplantation. Numerous articles have followed describing the immunosuppressive and rejection inhibiting properties of rapamycin, and clinical investigation has begun for the use of rapamycin in inhibiting rejection in transplantation in man.
Rapamycin alone (U.S. Pat. No. 4,885,171) or in combination with picibanil (U.S. Pat. No. 4,401,653) has been shown to have antitumor activity. R. R. Martel et al. [Can. J. Physiol. Pharmacol. 55, 48 (1977)] disclosed that rapamycin is effective in the experimental allergic encephalomyelitis model, a model for multiple sclerosis; in the adjuvant arthritis model, a model for rheumatoid arthritis; and effectively inhibited the formation of IgE-like antibodies.
The immunosuppressive effects of rapamycin have been disclosed in FASEB 3, 3411 (1989). Cyclosporin A and FK-506, other macrocyclic molecules, also have been shown to be effective as immunosuppressive agents, therefore useful in preventing transplant rejection [FASEB 3, 3411 (1989); FASEB 3, 5256 (1989); R. Y. Calne et al., Lancet 1183 (1978); and U.S. Pat. No. 5,100,899].
Rapamycin has also been shown to be useful in preventing or treating systemic lupus erythematosus [U.S. Pat. No. 5,078,999], pulmonary inflammation [U.S. Pat. No. 5,080,899], insulin dependent diabetes mellitus [Fifth Int. Conf. Inflamm. Res. Assoc. 121 (Abstract), (1990)], and smooth muscle cell proliferation and intimal thickening following vascular injury [Morris, R. J. Heart Lung Transplant 11 (pt. 2): 197 (1992)].
Mono- and diacylated derivatives of rapamycin (esterified at the 28 and 43 positions) have been shown to be useful as antifungal agents (U.S. Pat. No. 4,316,885) and used to make water soluble prodrugs of rapamycin (U.S. Pat. No. 4,650,803). Recently, the numbering convention for rapamycin has been changed; therefore according to Chemical Abstracts nomenclature, the esters described above would be at the 31- and 42-positions. U.S. Pat. No. 5,118,678 discloses carbamates of rapamycin that are useful as immunosuppressive, anti-inflammatory, antifungal, and antitumor agents. U.S. Pat. No. 5,100,883 discloses fluorinated esters of rapamycin. U.S. Pat. No. 5,118,677 discloses amide esters of rapamycin. U.S. Pat. No. 5,130,307 discloses aminoesters of rapamycin. U.S. Pat. No. 5,117,203 discloses sulfonates and sulfamates of rapamycin. U.S. Pat. No. 5,194,447 discloses sulfonylcarbamates of rapamycin.
U.S. Pat. No. 5,100,899 (Calne) discloses methods of inhibiting transplant rejection in mammals using rapamycin and derivatives and prodrugs thereof. Other chemotherapeutic agents listed for use with rapamycin are azathioprine, corticosteroids, cyclosporin (and cyclosporin A), and FK-506, or any combination thereof.
Rapamycin produces immunosuppressive effects by blocking intracellular signal transduction. Rapamycin appears to interfere with a calcium independent signalling cascade in T cells and mast cells [Schreiber et al. (1992) Tetrahedron 48:2545-2558]. Rapamycin has been shown to bind to certain immunophilins which are members of the FK-506 binding proteins (FKBP) family. In particular, Rapamycin has been shown to bind to the binding proteins, FKBP12, FKBP13, FKBP25 [Galat A. et al., (1992) Biochemistry 31(8);2427-2437 and Ferrera A, et al., (1992) Gene 113(1):125-127; Armistead and Harding, Ann. Reports in Med. Chem. 28:207-215, 1993], and FKBP52 [WO 93/07269].
Rapamycin is able to inhibit mitogen-induced T cell and B cell proliferation as well as proliferation induced by several cytokines, including IL-2, IL-3, IL-4 and IL-6 (reviewed by Sehgal et al., Med. Research Rev.14: 1-22, 1994). It can also inhibit antibody production. Rapamycin has been shown to block the cytokine-induced activation of p70.sup.S6 kinase which appears to correlate with Rapamycin's ability to decrease protein synthesis accompanying cell cycle progression (Calvo et al., Proc. Natl. Acad. Sci. USA, 89:7571-7575,1992; Chung et al., Cell 69:1227-1236, 1992; Kuo et al., Nature 358:70-73,1992; Price et al., Science 257:973-977, 1992). It also inhibits the activation of cdk2/cyclin E complex (Flanagan et al., Ann. N.Y.Acad. Sci, in press; Flanagan et al, Mol. Cell biol., in press; Flanagan et al., J.Cell Biochem. 17A:292, 1993). Rapamycin's effects are not mediated by direct binding to p70.sup.s6 kinase and cdk2/cyclin E, but by action of the Rapamycin-FKBP complex on upstream component(s) which regulate the activation status of the kinases.
It is generally accepted that the action of immunosuppressive drugs, such as Rapamycin, cyclosporine and FK506, is dependent upon the formation of a complex with their respective intracellular receptor proteins called immunophilins. While the binding of these immunosuppressants with their respective immunophilins inhibits the cis-trans peptidyl prolyl isomerase (PPIase) activity of immunophilins, PPIase inhibition is not sufficient to mediate the immunosuppressive activity (reviewed in Armistead and Harding, Annual Reports in Med. Chem, 28:207-215:1993). Two rapamycin analogs which are Diels Alder adducts, one with 4-phenyl-1,2,4-triazoline-3,5-dione, and the second with 4-methyl-1,2,4-triazoline-3,5-dione, bind to FKBP, inhibited its PPIase activity, yet they did not exhibit any detectable immunosuppressive activity. The phenyl-triazolinedione Diels Alder adduct at high molar excess has been shown to competitively inhibit rapamycin's effect on DNA synthesis in mitogen-stimulated murine thymocyte proliferation (Ocain et al., Biochem. Biophys. Res. Commun. 192:1340, 1993). Recent evidence suggests that the binary immunophilin-drug complex such as cyclophilin-cyclosporin A and FKBP-FK506 gains a new function that enables it to block signal transduction by acting on specific target proteins. The molecular target of both cyclophilin-cyclosporin A and FKBP-FK506 complexes such as has been identified as the Ca.sup.+2 /calmodulin dependent serine/threonine phosphatase calcineurin (J. Liu et al, Cell 66, 807, 1991; J. Liu et al, Biochemistry 31, 3896, 1992; W. M. Flanagan, et al., Nature 352, 803, 1992; McCaffrey et al., J. Biol. Chem. 268, 3747, 1993; McCaffrey et al., Science 262:750, 1993).
Rapamycin's antifungal and immunosuppressive activities are mediated via a complex consisting of Rapamycin, a member of the FK506 binding protein (FKBP) family and at least one additional third protein, called the target of Rapamycin (TOR). The family of FKBPs is reviewed by Armistead and Harding (Annual Reports in Med. Chem, 28:207-215:1993). The relevant FKBP molecule in Rapamycin's antifungal activity has been shown to be FKBP12 (Heitman et al., Science 253:905-909:1993). In mammalian cells, the relevant FKBPs are being investigated. Although two TOR proteins (TOR1 and TOR2) have been identified in yeast (Kunz et al., Cell 73:585-596:1993), the target of Rapamycin in human cells remains elusive. The carboxy terminus of yeast TOR2 has been shown to exhibit 20% identity with two proteins, the p110 subunit of phosphatidylinositol 3-kinase and VPS34, a yeast vacuolar sorting protein also shown to have PI 3K activity. However, J. Blenis et al. (AAI meeting, May, 1993) have reported that Rapamycin-FKBP12 complex does not directly mediate its effects on PDGF stimulated cells via the p110, p85 PI 3K complex.